The act of switching radio frequency signals in an integrated circuit is carried out by a Radio Frequency (RF) switch circuit. RF switches are well known in the art and provide a key building block in wireless systems. RF switches may be utilised in numerous applications such as mobile phones and wireless Local Area Networks (LANs). Such switches may include any number of switching elements which cooperate to control the flow of RF power between various circuit nodes. Performance metrics such as low insertion loss, high linearity, switching time, high isolation and power handling are critical in RF switch design. Generally an RF switch does not consist of the RF switching circuit alone. Typically an RF switch system is comprised of two domains; an RF domain which includes the switching elements and a Direct Current (DC) domain which includes control logic, bias generation and power management circuitry.
An RF switch may comprise any number of switching elements which control the flow of RF power between different points in the particular application. Generally, switching elements are comprised of transistors that are in a stacked configuration. The number of transistors in a stack is determined by the maximum RF voltage that can be developed across the complete stack and the maximum voltage that may be tolerated across an individual transistor without introducing limitations to either reliability or linearity performance of the device. RF ICs are subject to stringent linearity specifications which require tight limits on the level of distortion that a device may introduce on an RF signal. Linearity requirements may be expressed by specifying different parameters such as harmonics generation, intermodulation distortion (IMD2, IMD3) or intercept points, (IP2, IP3). Irrespective of how requirements are specified the linearity performance is determined by distortion introduced on RF signal by RF transistor stacks. Adoption of 4 G/LTE standards places ever increasing demands on linearity requirements of components such as RF switches. The RF transistor stack is becoming a limitation in achieving required linearity performance on SOI CMOS process.
There is therefore a need to provide an RF switch element which addresses at least some of the drawbacks of the prior art.